Not wishing to go round in circles but...
A parts dealer is going to buy bearings from a bearing supplier or wholesaler like Wassell who will buy from a bearing supplier.
If you buy the bearings from the supplier yourself, you can specify the manufacturer, the fit (std or C3) and the type of seals (none, rubber or metal)
If you buy from a parts dealer you do not know what you will get it could be a good make or something made in a Chinese sweat shop from recycled chopsticks